What is maths? "Maths is the study of ______"?

Math is the study of deductions from assumptions.

I've said it before, and I'll say it again (like a bleepin' broken record):

Mathematics is a collection of massively multi-player creative games that have collectively been played by tens of thousands of people on every inhabited continent since before the dawn of history. As befits such a game, mathematics has several different ways to score points:

1. Prove a theorem
2. Find a counterexample to a conjecture
3. Come up with a productive conjecture
4. Create a new subgame, perhaps inspired by something encountered in the world (a somewhat unusual and somewhat risky move, but often very rewarding)
5. Create a new variant of the game (a rare and risky move)
6. Teach others to play the game, who themselves go on to play it well

Mathematics: Science that studies by means of deductive reasoning the properties of abstract entities (numbers, geometric figures, functions, spaces, etc.) and the relationships established between them.

Translation of the definition of mathematics from the French dictionary Larousse